The translucent varieties of this stone, when viewed in a certain direction, sometimes exhibit a pearly and silvery play of colour. These are valued by jewellers, who cut them into a semi─globular form, and sell them under the name of moonstone. Those specimens are considered most estimable which, when cut in a very low oval, present the silvery spot in the centre of the stone. They are generally used for rings and brooches; and when set round with diamonds, their pearly lustre exhibits a striking and agreeable contrast with the brilliancy of that gem. Adularia is said to have been first discovered by an Italian mineralogist, near Mount St. Gothard, in Switzerland. He named it Adularia felspar, in the belief that the mountain on which he had found it was named Adula. This, however, was not the case; for Mount Adula is at some distance from St. Gothard, in the Grisons. This mineral has since been found in the granite of the island of Arran, in France, and Germany. The finest specimens are brought from Ceylon. ─────── ORDER II.–SOFT STONES. (Those which will not scratch Glass.) ─────── CLAY FAMILY. 114. Clay is a mixture of alumine (33) and silex (38), and is too well known to require much description. It is opaque, has an earthy texture, is about twice as heavy as water, when moistened is very ductile, adheres slightly to the tongue; and with its peculiar smell (called clayey) every one is acquainted. 115. _COMMON CLAY, or POTTER’s CLAY, which is found in nearly every country of the world, is sometimes white, has a blue or yellowish tinge, or is brown or reddish._